Linear polyesters such as poly(alkylene terephthalates) are well known commercially available polymers. They have many valuable characteristics including strength, toughness, high gloss and solvent resistance. Linear polyesters are conventionally prepared by the reaction of a diol with a functional derivative of a dicarboxylic acid, typically a diacid halide or ester. Further, the above-described polyesters may be fabricated into articles by a number of well known techniques including injection and roto molding and extrusion.
In recent years, macrocyclic polyester oligomers have been developed and desired since they have unique properties which make them attractive as matrices for polymer composites. Such desired properties stem from the fact that macrocyclic polyester oligomers exhibit low viscosities, allowing them to impregnate a dense fibrous preform easily. Furthermore, such macrocyclic polyester oligomers melt and polymerize at temperatures well below the melting point of the resulting polymer. Thus, melt flow, polymerization and crystallization can occur isothermally and, therefore, the time and expense required to thermally cycle a tool is favorably reduced.
Previously known methods for producing macrocyclic polyester oligomers typically employ amine catalysts and corrosive acid halides such as terephthaloyl chloride. Such methods are often undesirable since they require environmentally unfriendly halides and expensive recycling steps associated with the formation of byproduct amine salts. Other methods employ cumbersome steps including the distillation of solvents over calcium hydride.
The instant invention, therefore, is directed to a novel process for producing macrocyclic polyester oligomers, wherein the method comprises the step of subjecting polyesters to catalysts, and organic solvents which are substantially free of oxygen and water.